Conventional e-bike motor output power control is based on an input to the motor controller of the degree of rotation of the hand throttle, which is moved by the rider. This functions satisfactorily where the e-bike is solely or primarily powered by the electric motor. But a hand throttle is difficult to operate when the electric motor is configured to merely assist the rider in pedaling.
In some regions, like Europe, motor power is treated as an assisting power—PAS (Pedal Assist System)—to help the person ride the e-bike more easily, and not the primary means of powering the bike. The PAS is merely an electric motor assist to the rider, so PAS is used to make riding the e-bike more like a regular bike.
In PAS systems, if biker does not pedal, the motor does not generate any output power. Speed PAS is based on biker's pedaling speed. When e-bike goes uphill, the e-bike rider will need more power from the electric motor, but they cannot get that power from a Speed PAS system because their pedaling speed is slower due to going uphill. Therefore, a torque sensor PAS system is required to sense the rider's pedaling power, so that the control system can control the motor's output power appropriately.
However, if rider's two legs stand on both pedals, the torque force will be very high. In this situation, it would be dangerous for the assist motor to generate its highest power. Therefore, the bike's crank speed and crank position need to be taken into account for safely and effectively controlling the assist motor for the bike.
Providing torque and crank position data to the motor controller is a challenge. A wireless transmission means can be used. However, not all of the e-bike controllers on the market have wireless receivers. Providing an aftermarket wireless receiver for the motor controller is not a satisfactory solution either since it would require the manufacturer or rider to modify their e-bike controller hardware and software to talk to the aftermarket wireless receiver. That requires additional cost and time to adapt the motor controller to an aftermarket wireless system for receiving the torque and crank position data. Most of e-bike manufacturers are not willing to take extra steps to modify their e-bike controller hardware and software.
Another issue is that torque sensors alone are not good enough to make a torque PAS because it is necessary to detect the exact crank position to send the right control signals to control e-bike controller. Some torque sensor PAS vendors put torque sensing component(s) on pedal axle to sense the twisting power caused by both legs. But this makes it difficult to sense the crank positions and the rider's intention cannot be easily discerned. For example, reverse pedaling means the rider wants to brake; both cranks in parallel to ground position means biker is resting and the motor can adjust its power output correspondingly; when left crank is at the lowest position and right crank in upper position, the crank can detect that the rider is in a dismounting position so that motor can adjust accordingly, and so on.
Further, powering the crank sensors presents difficulties. To avoid twisting wires caused by moving crank, adding a battery on the crank itself is one way to provide power. But battery life limits the use of the smart crank system. Recharging or replacing batteries is inconvenient and can be expensive.
Therefore, there remains a need to provide an improved electric power assist for e-bikes without extra efforts to modify the e-bike controller. There is also a need to provide smart crank control for e-bikes.